The invention relates to head assemblies for nuclear reactor pressure vessels (“RPVs”) and more particularly to integrated head assemblies that can be transported as integral units.
Commercial pressurized water nuclear power plants are operated to produce electric power during fuel cycles that extend for about one to two years and then are shutdown for scheduled refueling and maintenance outages that extend for up to about a month or more. At the beginning of these outages, removable RPV closure heads and overhead equipment and cooling air ductwork associated with the RPVs, including control rod drive mechanisms (“CRDMs”), CRDM cooling systems, CRDM seismic support platforms and missile shields (which collectively are known in the industry as the “head assemblies”) must be disconnected and/or removed in order to gain access to the fuel assemblies disposed in the interior portions of the RPVs. Then, at the end of the outages, the head assemblies must be re-assembled before starting the following fuel cycles. See, e.g., FIG. 1 of U.S. Pat. No. 4,678,623, which discloses a prior art assembly including a concrete missile shield. The many disassembly and re-assembly steps and sub-steps tend to be complex, costly to perform and require long times on critical path schedules in radioactive environments. Updated head assembly designs permit these structures to be transported as integral units to facilitate more efficient and safer outages. However, these newer designs include modified structures for redirecting the cooling air that completely or partially enclose the CRDMs and thereby hinder access to the CRDMs for repair and maintenance purposes. See, e.g., U.S. Pat. Nos. 4,678,623; 4,828,789; 5,742,652 and 6,061,414, which are incorporated herein for their disclosures of various modular, integrated and simplified head assemblies.
While the development of integrated head assemblies and the other patented improvements have facilitated faster, safer outages, the nuclear industry is constantly searching for more efficient and safer ways of operating, refueling and maintaining their plants.